Receiving apparatus, transmitting apparatus, reception method, and transmission method

ABSTRACT

A reception unit receives data from communication apparatuses. A transmission unit transmits data to the communication apparatuses. A control unit determines, in an adaptive way, which modulation and coding schemes to use to transmit and receive data. At a first stage, a modulation and coding scheme with a low transmission rate or a modulation and coding scheme that minimizes power requirements is selected from among a plurality of candidates therefor. At a second stage, the modulation and coding scheme of at least one of the communication apparatuses is changed to another scheme having a higher transmission rate, when it is impossible to allocate sufficient resources for the modulation and coding schemes selected at the first stage.

This application is a continuation of U.S. application Ser. No.12/887,937, filed Sep. 22, 2010, now U.S. Pat. No. 8,254,501, which is acontinuation, filed under 35 U.S.C. §III(a), of InternationalApplication PCT/JP2008/056386, filed Mar. 31, 2008.

FIELD

The present invention relates to a receiving apparatus, transmittingapparatus, reception method, and transmission method.

BACKGROUND

Point-to-multipoint (1:n) communications systems are now prevalent inthe field of wireless communication, which allow one device tocommunicate with two or more devices simultaneously. The existingstandards for such 1:n wireless communication include, for example, IEEE802.16d defining fixed wireless access systems and IEEE 802.16e definingmobile wireless access systems (see, for example, the followingLiteratures 1 and 2). In this section, the term “radio base station” isused to refer to a device that can communicate simultaneously with aplurality of devices, and the term “mobile stations” to refer to thedevices that communicate with the radio base station.

Literature 1: The Institute of Electrical and Electronics Engineers(IEEE), “IEEE Standard for Local and Metropolitan Area Networks Part 16:Air Interface for Fixed Broadband Wireless Access Systems,” IEEE802.16-2004.

Literature 2: The Institute of Electrical and Electronics Engineers(IEEE), “IEEE Standard for Local and Metropolitan Area Networks Part 16:Air Interface for Fixed and Mobile Broadband Wireless Access Systems,”IEEE 802.16e-2005.

Many of the 1:n wireless communication systems are designed to operateunder the primary control of radio base stations. For example, theallocation of radio resources used in communication between a radio basestation and mobile stations is centrally managed by the radio basestation. Here the radio base station may use an adaptive modulation andcoding (AMC) technique to enhance the efficiency of wirelesscommunication. With AMC, the radio base station dynamically determineswhich modulation and coding scheme (MCS) to use to communicate with amobile station, depending on the current quality of radio links betweenthe radio base station and the mobile station.

A modulation and coding scheme specifies, for example, a modulationmethod, a coding method, and a coding rate. By combining differentoptions for those elements, a number of candidates for the modulationand coding scheme are made available. Each such candidate has adifferent transmission rate, or in other words, each candidatetransports a different amount of data per unit radio resource. The radiobase station is supposed to select an appropriate modulation and codingscheme for individual mobile stations, from among those having differenttransmission rates. For example, it may be appropriate to select amodulation and coding scheme with a high transmission rate for mobilestations having a high radio link quality. It may also be appropriate toselect a modulation and coding scheme with a low transmission rate formobile stations having a low radio link quality, because such mobilestations would otherwise encounter more frequent data errors andconsequent instability of communication.

Mobile communications systems may use multicarrier modulationtechniques, in which case the modulation method and coding rate areselected based on power levels of subcarriers. Specifically, the radiobase station measures the power level of each received subcarrier signaland selects a set of subcarriers capable of achieving a certain grade oftransmission rate. The radio base station then determines whichmodulation method and coding rate to use, according to the receive powerlevel of the selected subcarriers (see, for example, Japanese Laid-openPatent Publication No. 2003-304214).

While the modulation and coding schemes selected in the above-describedadaptive modulation and coding may be advantageous to the radio basestation itself, it does not always mean that the same schemes are alsoadvantageous to mobile stations.

More specifically, the radio base station will be able to transmit thesame amount data with a fewer radio resources and thus increase thenumber of simultaneous communication sessions, by applying a modulationand coding scheme with a high transmission rate to mobile stations witha high link quality. This means that, from the viewpoint of radio basestations, it is more advantageous to select a modulation and codingscheme with as high a transmission rate as possible.

The mobile stations, on the other hand, have to raise their output powerto transmit data to the radio base station by using a modulation andcoding scheme with a high transmission rate. This leads to an increasedpower consumption in the mobile stations. The use of a modulation andcoding scheme with a high transmission rate also affects the receptionof data from the radio base station. That is, the probability ofsuccessful reception is reduced as the transmission rate increases. Thismeans that, from the viewpoint of mobile stations, it is moreadvantageous to select a modulation and coding scheme with a lowertransmission rate, even under the condition of good radio link quality.

SUMMARY

According to an aspect of the invention, a receiving apparatus thatspecifies modulation and coding schemes respectively for a plurality oftransmitting apparatuses and receives data that the transmittingapparatuses transmit by using the specified modulation and codingschemes, the receiving apparatus includes: a control unit that collectsinformation on the amount of data to be transmitted by each transmittingapparatus; selects, for each individual transmitting apparatus, amodulation and coding scheme that transports a smaller amount of dataper unit resource than the other modulation and coding schemes, fromamong a plurality of candidates for the modulation and coding schemes;determines whether necessary resources are allocable for reception ofthe data to be transmitted from the transmitting apparatuses, based onthe amount of the data to be transmitted and the selected modulation andcoding schemes; and when the resources are unallocable, changes thecurrently selected modulation and coding scheme of at least one of thetransmitting apparatuses to another modulation and coding scheme thattransports a larger amount of data per unit resource than the currentlyselected modulation and coding scheme.

The objects and advantages of the invention will be realized andattained by means of the elements and combinations particularly pointedout in the claims.

It is to be understood that both the forgoing general description andthe following detailed description are exemplary and explanatory and arenot restrictive of the invention, as claimed.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 provides an overview of the present embodiment;

FIG. 2 illustrates a system configuration according to the presentembodiment;

FIG. 3 is a functional block diagram of a radio base station;

FIG. 4 illustrates a data structure of radio frames;

FIG. 5 illustrates a data structure of UL-MAP data;

FIG. 6 illustrates a data structure of DL-MAP data;

FIG. 7 illustrates a data structure of a profile candidate table;

FIG. 8 illustrates a data structure of a mobile station data table;

FIG. 9 illustrates a data structure of a data traffic size table;

FIG. 10 is a sequence diagram illustrating an example process flow oftransmission power control;

FIG. 11 is a sequence diagram illustrating an example process flow ofbandwidth allocation control;

FIG. 12 is a sequence diagram illustrating an example process flow of DLradio quality measurement;

FIG. 13 is a flowchart illustrating a first UL profile setup process;

FIG. 14 illustrates a data structure of a power requirement table;

FIG. 15 illustrates a data structure of a UL profile setup table;

FIG. 16 schematically illustrates a flow of the first UL profile setupprocess;

FIG. 17 is a flowchart of a second UL profile setup process;

FIG. 18 schematically illustrates a flow of the second UL profile setupprocess;

FIG. 19 is a flowchart of a first DL profile setup process;

FIG. 20 illustrates a data structure of a DL profile setup table;

FIG. 21 schematically illustrates a flow of the first DL profile setupprocess;

FIG. 22 is a flowchart of a second DL profile setup process; and

FIG. 23 schematically illustrates a flow of the second DL profile setupprocess.

DESCRIPTION OF EMBODIMENT(S)

The present embodiment will now be described in detail below withreference to the accompanying drawings.

FIG. 1 provides an overview of the present embodiment. Thecommunications system illustrated in FIG. 1 includes communicationapparatuses 1, 2, 3, and 4. The communication apparatus 1 cancommunicate with other communication apparatuses 2, 3, and 4simultaneously. For example, the communication apparatus 1 may be aradio base station, and the communication apparatuses 2, 3, and 4 may bemobile stations. The communication apparatus 1 is formed from areception unit 1 a, a transmission unit 1 b, and a control unit 1 c.

The reception unit 1 a receives signals from communication apparatuses2, 3, and 4, which carry payload data and control information. Thereception unit 1 a then demodulates and decodes the received signals soas to extract the payload data and control information. During thiscourse, the control unit 1 c specifies several parameters indicatingwhich modulation and coding schemes to use, depending on with whichapparatus the communication apparatus 1 is to communicate. The receptionunit 1 a executes demodulation and decoding operations by using themethods according to the specified parameters. When control informationis extracted, the reception unit 1 a supplies that extracted informationto the control unit 1 c. What is received as control information mayinclude, for example, transmission power levels of the communicationapparatuses 2, 3, and 4 and measurement results of receive signalquality of the same. The control information may also includeinformation indicating the amount of data that the communicationapparatuses 2, 3, and 4 are to transmit.

The transmission unit lb performs modulation and coding of payload dataand control information to be transmitted to the communicationapparatuses 2, 3, and 4, thereby producing transmit signals. Thetransmission unit 1 b then transmits those transmit signals to thecommunication apparatuses 2, 3, and 4. During this course, the controlunit 1 c specifies several parameters indicating which modulation andcoding schemes to use, depending on with which apparatus thecommunication apparatus 1 is to communicate. The transmission unit 1 bexecutes modulation and coding by using the methods according to thespecified parameters. What is transmitted as control information mayinclude information specifying modulation and coding schemes that thecommunication apparatuses 2, 3, and 4 are supposed to use when theytransmit data.

The control unit 1 c manages resources used for uplink communication(i.e., the communication in the direction from the communicationapparatuses 2, 3, and 4 to the communication apparatus 1) to control thereception unit 1 a and its reception operation. Also the control unit 1c manages resources used for downlink communication (i.e., thecommunication in the direction from the communication apparatus 1 to thecommunication apparatuses 2, 3, and 4) to control the transmission unit1 b and its transmission processing. During this course, the controlunit 1 c controls the operation of adaptive modulation and coding. Morespecifically, the control unit 1 c dynamically determines whichmodulation and coding scheme to use for communication with eachindividual communication apparatus 2, 3, and 4, by consulting thecontrol information supplied from the reception unit 1 a as necessary.

In uplink communication, the control unit 1 c first makes a provisionalselection of a modulation and coding scheme for each individualcommunication apparatus 2, 3, and 4 from among a plurality of candidatemodulation and coding schemes, according to a first selection method. Anexample of the first selection method is to choose a modulation andcoding scheme with the lowest transmission rate. Another example of thefirst selection method is to choose a modulation and coding scheme thatminimizes the total transmission power of communication apparatuses 2,3, and 4. Subsequently the control unit 1 c determines whether it ispossible to allocate resources necessary for receiving all data that thecommunication apparatuses 2, 3, and 4 are going to transmit, assumingthe use of the modulation and coding scheme that has been provisionallyselected with the first selection method.

When it is found possible to allocate such resources, the control unit 1c chooses and uses the provisionally selected modulation and codingscheme as the final selection. When it is found impossible to allocateall necessary resources, the control unit 1 c uses a second selectionmethod to change the modulation and coding scheme of at least one of thecommunication apparatuses 2, 3, and 4. One example of the secondselection method is to select new modulation and coding schemes byraising the transmission rate in a stepwise manner, with respect to theprovisional modulation and coding scheme, until it is determined thatall necessary resources can be allocated. Another example of the secondselection method is to select a modulation and coding scheme with thehighest transmission rate of all those that can be applied. The controlunit 1 c then applies the modulation and coding scheme that it hasselected with the second selection method. It is noted that the controlunit 1 c determines which communication apparatuses should be subjectedto the change of modulation and coding schemes. For example, the controlunit 1 c may select a communication apparatus with a smallertransmission power level in preference to others.

Also in downlink communication, the control unit 1 c first makes aprovisional selection of a modulation and coding scheme for eachindividual communication apparatus 2, 3, and 4 from among a plurality ofcandidate modulation and coding schemes, according to a first selectionmethod. For example, the first selection method may be to choose amodulation and coding scheme with the lowest transmission rate.Subsequently the control unit 1 c determines whether it is possible toallocate resources necessary for transmitting all data destined for thecommunication apparatuses 2, 3, and 4, assuming the use of theprovisional modulation, and coding schemes that it has selected with thefirst selection method.

When it is found possible to allocate such resources, the control unit 1c chooses and uses the provisional modulation and coding schemes as thefinal selection. When it is found impossible to allocate all necessaryresources, the control unit 1 c uses a second selection method to changethe modulation and coding scheme of at least one of the communicationapparatuses 2, 3, and 4. The second selection method described above forthe uplink communication may serve for this downlink communication aswell. The control unit 1 c then applies the modulation and coding schemethat it has selected with the second selection method. It is noted that,to apply the change of modulation and coding schemes, the control unit 1c may select a communication apparatus with a higher level of receivesignal quality in preference to others.

The above description assumes that the communication apparatus 1incorporates both receive and transmit functions. It is also possible,however, to implement these functions separately in a receivingapparatus and a transmitting apparatus. When this is the case, thereceiving apparatus and transmitting apparatus may have their owncontrol units for adaptive modulation and coding. The above descriptionalso assumes that different modulation and coding schemes are selectedfor uplink communication and downlink communication. The control unit 1c may, however, be configured to use the same modulation and codingscheme for both uplink communication and downlink communication.

In operation of the above-described communications system, a provisionalmodulation and coding scheme is selected for uplink communication ofeach communication apparatus 2, 3, and 4, from among a plurality ofcandidate modulation and coding schemes, in favor of those having lowertransmission rates or smaller transmission power levels. Then based onthe amount of data to be transmitted from each communication apparatus2, 3, and 4, as well as on the selected provisional modulation andcoding schemes, it is determined whether resources can be allocated forsimultaneous reception of data from those communication apparatuses 2,3, and 4. When it is not possible to allocate all necessary resources,the provisional modulation and coding scheme of at least one of thecommunication apparatuses is changed to another scheme that has a highertransmission rate.

For downlink communication, a provisional modulation and coding schemeis selected for each communication apparatus 2, 3, and 4 from among aplurality of candidate modulation and coding schemes, in favor of thosehaving lower transmission rates. Then based on the amount of data to betransmitted to individual communication apparatuses 2, 3, and 4, as wellas on the selected provisional modulation and coding schemes, it isdetermined whether resources can be allocated for simultaneoustransmission of data to those communication apparatuses 2, 3, and 4.When it is not possible to allocate all necessary resources, theprovisional modulation and coding scheme of at least one of thecommunication apparatuses is changed to another scheme that has a highertransmission rate.

The above-described features enable the communication apparatus 1 tochoose more appropriate modulation and coding schemes, considering theviewpoint of other communication apparatuses 2, 3, and 4 with which thecommunication apparatus 1 is to communicate. In other words, thecommunication apparatus 1 can select modulation and coding schemes thatminimize the transmission rate per unit resource and total transmissionpower in uplink communication while ensuring allocation of resourcesthat the communication apparatuses 2, 3, and 4 require. This featurealleviates the burden on the communication apparatuses 2, 3, and 4.Similarly, the communication apparatus 1 can select modulation andcoding schemes for downlink communication which minimize thetransmission rate per unit resource while ensuring allocation ofresources necessary for data transmission to the communicationapparatuses 2, 3, and 4. This feature increases the probability ofsuccessful reception of signals at the receiving communicationapparatuses 2, 3, and 4.

The specifics of the present embodiment will now be described in detailbelow with reference to the accompanying drawings.

FIG. 2 illustrates a system configuration according to the presentembodiment. This wireless communications system according to the presentembodiment includes a radio base station 100 and mobile stations 200,200 a, 200 b, and 200 c. The mobile stations 200, 200 a, 200 b, and 200c are located in the radio coverage area (cell) of the radio basestation 100. While not illustrated in FIG. 2, the radio base station 100is connected to its upper-level stations and other radio base stationsvia wired or wireless links.

The radio base station 100 is a wireless communication device capable ofcommunicating simultaneously with multiple mobile stations 200, 200 a,200 b, and 200 c via radio waves. More specifically, the radio basestation 100 can receive user data and control information that themobile stations 200, 200 a, 200 b, and 200 c transmit by sharing asingle radio frame. The radio base station 100 can also transmit userdata and control information addressed to the mobile stations 200, 200a, 200 b, and 200 c by using a single radio frame.

The mobile station 200, 200 a, 200 b, and 200 c are wirelesscommunication devices (e.g., cellular phones) capable of communicatingwith the radio base station 100 via radio waves when they are in thecell of the radio base station 100. When they have user data or controldata to transmit, the mobile stations 200, 200 a, 200 b, and 200 creceive an allocation of radio resources from the radio base station 100and transmit such data using the allocated radio resources. The mobilestations 200, 200 a, 200 b, and 200 c also receive signals from theradio base station 100 and extract therefrom user data and controlinformation when they find such data and information in the receivedsignals.

The wireless communications system according to the present embodimentcontrols adaptive modulation and coding. More specifically, the radiobase station 100 selects an appropriate modulation and coding scheme foreach individual mobile station 200, 200 a, 200 b, and 200 c, dependingon the current condition of their communication links. Selection ofmodulation and coding schemes is made separately for uplinkcommunication and downlink communication. It is noted that the presentembodiment assumes conformity to the IEEE 802.16e standard in wirelesscommunication between the radio base station 100 and mobile stations200, 200 a, 200 b, and 200 c.

FIG. 3 is a functional block diagram of a radio base station. This radiobase station 100 includes a transmit-receive antenna 111, an antennaduplexer 112, a reception unit 121, a code reception unit 122, a controlinformation extraction unit 123, a packet generation unit 124, a controlunit 130, a communication unit 141, a packet discrimination unit 151, apacket buffer 152, a control information generation unit 153, a mapgeneration unit 154, a PDU generation unit 155, and a transmission unit156.

The transmit-receive antenna 111 is an antenna used for bothtransmission and reception of signals. Specifically, thetransmit-receive antenna 111 radiates radio waves of transmit signalssupplied from an antenna duplexer 112. The transmit-receive antenna 111also receives radio wave signals and supplies them to the antennaduplexer 112.

The antenna duplexer 112 is a device that separates transmit signals andreceive signals from each other, which may simply be called a duplexer.Specifically, the antenna duplexer 112 supplies transmission signalsfrom the transmission unit 156 to the transmit-receive antenna 111, aswell as routing receive signals from the transmit-receive antenna 111 tothe reception unit 121. The antenna duplexer 112 filters receivesignals, as well as preventing transmit signals from flowing into thereceiver circuitry.

Out of the receive signals supplied from the antenna duplexer 112, thereception unit 121 extracts signals in Ranging region, a region of radioframes, and provides them to the code reception unit 122. The receptionunit 121 also demodulates and decodes the received signals according tothe demodulation method and decoding method specified by the controlunit 130. The resulting data is supplied to the control informationextraction unit 123.

The code reception unit 122 compares a signal received from thereception unit 121 with a plurality of ranging codes, thus determiningwhich ranging code the received signal indicates. The code receptionunit 122 also analyzes the received signal to measure the receive powerlevel, uplink radio quality, receive timing offset, and the like. Thecode reception unit 122 then sends the result of its ranging codedetermination, together with those various measurements, to the controlunit 130.

The control information extraction unit 123 extracts control informationand user data out of the data supplied from the reception unit 121. Thecontrol information extraction unit 123 outputs the extracted user datato the packet generation unit 124, while supplying the extracted controldata to the control unit 130. The extracted control information mayinclude parameters indicating the current transmission power level ofeach mobile station 200, 200 a, 200 b, and 200 c, the measurement resultof downlink quality, and allocation requests for uplink radio resources.

The packet generation unit 124 produces a data packet by compiling userdata received from the control information extraction unit 123. Thisdata packet conforms to a prescribed format used to transport databetween the radio base station 100 and its upper-level station or peerradio base stations. The packet generation unit 124 then sends theproduced data packet to the communication unit 141.

The control unit 130 controls the overall operation of signaltransmission and reception in the radio base station 100. For example,the control unit 130 controls allocation of uplink radio resources basedon ranging code information provided from the code reception unit 122and control information provided from the control information extractionunit 123. The control unit 130 also controls allocation of downlinkradio resources based on the current occupancy of the packet buffer 152storing data packets. The control unit 130 then notifies the mapgeneration unit 154 of the result of radio resource allocation.

The control unit 130 controls the process of adaptive modulation andcoding individually for uplink communication and downlink communication,depending on the radio link quality and transmission power level ofindividual mobile stations 200, 200 a, 200 b, and 200 c. The controlunit 130 informs the reception unit 121, map generation unit 154, andtransmission unit 156 of the determined modulation and coding schemes.Otherwise, the control unit 130 performs various control operations and,if necessary, commands the control information generation unit 153 toproduce control information.

The communication unit 141 is a network interface that transmits andreceives data packets to/from upper-level stations or other wirelesscommunication devices. Specifically, the communication unit 141 receivesdata packets from the packet generation unit 124 and transmits them tothe network. The communication unit 141 also receives data packets fromthe network and supplies them to the packet discrimination unit 151.

The packet discrimination unit 151 examines the header of data packetssupplied from the communication unit 141, thereby identifying theirdestinations and data types. According to this identification result,the packet discrimination unit 151 stores the data packets inappropriate locations in the packet buffer 152.

The packet buffer 152 is a buffer memory for temporarily storing datapackets received from upper-level stations and other radio basestations. Specifically, the packet buffer 152 provides a plurality ofstorage spaces to sort the data packets according to their destinationsand data types. The packet buffer 152 outputs those data packets inresponse to access requests from the PDU generation unit 155.

The control information generation unit 153 produces control informationfor the mobile stations 200, 200 a, 200 b, and 200 c in response tocommands from the control unit 130. The produced control information mayinclude, among other things, acknowledgment of received user data andcontrol information, an update command for transmission power level andtransmit timing, current transmission power levels, and a request forquality measurement results. Then the control information generationunit 153 supplies the produced control information to the PDU generationunit 155, as well as notifying the map generation unit 154 that thecontrol information has been produced.

The map generation unit 154 produces DL-MAP data, based on informationfrom the control unit 130 and control information generation unit 153.This DL-MAP data describes allocation of downlink radio resources. Themap generation unit 154 also produces UL-MAP data, based on informationfrom the control unit 130. This UL-MAP data describes allocation ofuplink radio resource. The produced DL-MAP data and UL-MAP data are sentto the PDU generation unit 155.

The PDU generation unit 155 consults the DL-MAP data supplied from themap generation unit 154 so as to determine which data packet to transmitnext, and then extracts the determined data packet from the packetbuffer 152. The PDU generation unit 155 then produces data of a radioframe by using DL-MAP data and UL-MAP data supplied from the mapgeneration unit 154 in addition to data packets supplied from the packetbuffer 152. Radio frame is the protocol data unit (PDU) in the radiolink section. The PDU generation unit 155 then sends the produced radioframe data to the transmission unit 156.

The transmission unit 156 encodes and modulates the radio frame datasupplied from the PDU generation unit 155, according to the modulationmethod and coding method specified by the control unit 130. Thetransmission unit 156 then outputs the resulting transmit signals to theantenna duplexer 112.

FIG. 4 illustrates a data structure of radio frames. This radio frame ofFIG. 4 is used in wireless communication between the radio base station100 and mobile stations 200, 200 a, 200 b, and 200 c. According to thepresent embodiment, the proposed wireless communications system offershalf-duplex communication using a time-division duplex (TDD) technique.More specifically, one radio frame is divided into two time periods. Thefirst time period is used as a DL subframe for downlink communication,and the second time period is used as a UL subframe for uplinkcommunication.

The DL subframe begins with a preamble region which acts as a delimiterbetween radio frames. This preamble region carries prescribed preamblesignals. The preamble region is followed by DL-MAP region, which is usedto transmit DL-MAP data. The DL-MAP area is then followed by DL-Burstregion. A part of this DL-Burst region is dedicated as UL-MAP region totransmit UL-MAP data. The rest of the DL-Burst region is assigned fortransmission of user data and control information to each mobilestation. The current allocation of DL-Burst region is described in theDL-MAP data.

The UL subframe has a ranging region to transmit ranging codes. Mobilestations 200, 200 a, 200 b, and 200 c are allowed to use the rangingregion to transmit their ranging codes without asking permission of theradio base station 100. The rest of the UL subframe is assigned asUL-Burst region for the purpose of transmission of user data and controlinformation from mobile stations 200, 200 a, 200 b, and 200 c to theirradio base station 100. The current allocation of UL-Burst region isdescribed in the UL-MAP data.

The resources in a radio frame are managed in units of subchannels alongthe frequency axis, and in units of symbols along the time axis. Theterm “subchannel” refers to a prescribed number of subcarriers beingbundled together. Allocation of such resources to mobile stations 200,200 a, 200 b, and 200 c is performed on an individual slot basis. Slotis a portion of the resources that has a frequency range of a singlesubchannel and a time period across a prescribed number of symbols(e.g., three symbols).

FIG. 5 illustrates a data structure of UL-MAP data. UL-MAP data istransmitted by using UL-MAP region in a DL subframe. Specifically,UL-MAP data includes the following data items: Connection Identifier(CID), Uplink Interval Usage Code (UIUC), Duration, and RepetitionCoding Indication. UL-MAP region carries the values of these data itemsfor each different mobile station 200, 200 a, 200 b, and 200 c.

CID is a 16-bit identifier assigned to each mobile station connected tothe radio base station 100. UIUC is a 4-bit identifier indicating whichmodulation and coding scheme the mobile station identified by CID issupposed to use in its uplink communication. Duration is a 10-bitnumerical value indicating the radio resource (slot) assigned to themobile station identified by CID. Repetition Coding Indication is a bitstring used to control the operation of repetitively transmitting thesame data (repetition coding). Repetition Coding Indication is two bitsin length.

FIG. 6 illustrates a data structure of DL-MAP data. DL-MAP data istransmitted by using the DL-MAP region in a DL subframe. Specifically,DL-MAP data includes the following data items: CID, Downlink IntervalUsage Code (DIUC), Symbol Offset, Subchannel Offset, Boosting, No.Symbols, No. Subchannels, and Repetition Coding Indication. DL-MAPregion carries the values of these data items for each different mobilestation 200, 200 a, 200 b, and 200 c.

As already noted, CID is an identifier assigned to each mobile stationconnected to the radio base station 100. DL-MAP data may specify one ormore CIDs. DIUC is a 4-bit identifier indicating which modulation andcoding scheme the mobile station identified by CID is supposed to use inits downlink communication. Symbol Offset is a 6-bit numerical valuepointing to the leading symbol of a region assigned to the mobilestation identified by CID. Subchannel Offset is a 6-bit numerical valuepointing to the topmost subchannel of a region allocated to the mobilestation identified by CID. The combination of Symbol Offset andSubchannel Offset is used to identify the leading slot of an allocatedregion.

Boosting is a bit string used for boost control, i.e., the controloperation of temporarily raising the transmission power level. Boostingis three bits in length. No. Symbols is a 7-bit numerical valuerepresenting the number of symbols allocated to the mobile stationidentified by CID. No. Subchannels is a 6-bit numerical valuerepresenting the number of subchannels allocated to the mobile stationidentified by CID. Repetition Coding Indication is, as already noted, abit string used to control repetition processing.

Data transmission of DL-Burst and UL-Burst regions is performed withspecific modulation and coding schemes. The definition of whichmodulation and coding scheme to use is called a “burst profile.”Selecting a specific burst profile means determining a specific set ofmodulation method, coding method, and coding rate for data transmission.The radio base station 100 and mobile stations 200, 200 a, 200 b, and200 c share the information about candidates for burst profile beforethey start data transmission on DL-Burst region and UL-Burst region.

FIG. 7 illustrates a data structure of a profile candidate table. Theprofile candidate table 131 of FIG. 7 is stored in an appropriate memoryunder the management of the control unit 130. Specifically, the profilecandidate table 131 is formed from the following data fields: UIUC/DIUC,Modulation and Coding Scheme, and SINR Threshold. The field valuesarranged in the horizontal direction are associated with each other,thus forming a single entry of burst profile.

The UIUC/DIUC field contains an identifier of a burst profile(modulation and coding scheme). This identifier corresponds to what havebeen described above as UIUC and DIUC. The modulation and coding schemefield contains a character string indicating a specific modulationmethod, coding method, and coding rate. The SINR threshold fieldcontains a value of signal to interference and noise ratio (SINR) whichrepresents the lower limit of radio communication quality required so asto apply the corresponding burst profile (modulation and coding scheme).

The choices for the modulation method include: quadrature phase shiftkeying (QPSK) and 16-level quadrature amplitude modulation (16QAM). Thechoices for the coding method include: convolutional code (CC),convolutional turbo code (CTC), and block turbo code (BTC). The choicesfor the coding rate include: 1/2 (ratio of 1:1 between information bitsand check bits), 2/3 (ratio of 2:1 between information bits and checkbits), and 3/4 (ratio of 3:1 between information bits and check bits).The transmission rate is a function of those choices of modulationmethod, coding method, and coding rate. The profile candidate table 131arranges its entries in descending order of transmission rates andassigns their identifiers accordingly.

The profile candidate table 131 has been created by an administrator andregistered in the radio base station 100. For example, the profilecandidate table 131 has an entry with UIUC/DIUC=2, Modulation and CodingScheme=QPSK(CC)2/3, and SINR Threshold=5 dB. This entry means that theradio communication quality has to be as good as SINR of 5 dB or more inorder to transmit data with the modulation and coding scheme that usesQPSK modulation, CC coding, and 2/3 coding rate.

It is noted that the present embodiment uses the same set of burstprofiles for both uplink communication and downlink communication.Therefore, UIUC and DIUC have substantially the same meaning. It is alsopossible, however, to provide separate sets of burst profiles for uplinkcommunication and downlink communication. When this is the case, twotables similar to the above-described profile candidate table 131 arecreated, one for uplink communication and the other for downlinkcommunication.

FIG. 8 illustrates a data structure of a mobile station data table. Themobile station data table 132 of FIG. 8 is stored in an appropriatememory under the management of the control unit 130. This mobile stationdata table 132 is formed from the following data fields: Mobile StationID, Transmission Power, Maximum Transmission Power, and SINR. The fieldvalues arranged in the horizontal direction are associated with eachother, thus forming a single entry describing a specific mobile station.

The mobile station ID field contains an identifier of a specific mobilestation 200, 200 a, 200 b, and 200 c. The foregoing CID may serve asthis mobile station ID. The transmission power field contains anumerical value indicating the current transmission power level of eachmobile station. More specifically, this value represents thetransmission power per subchannel in the case where a modulation andcoding scheme with the lowest transmission rate (e.g., QPSK(CC)1/2) isapplied. The maximum transmission power field contains a numerical valueindicating a transmission power level that can be achieved by increasingthe output up to its maximum point. The SINR field indicates a downlinkSINR value measured by the corresponding mobile station.

The control unit 130 updates the mobile station data table 132 as theneed arises, based on control information that the mobile stations 200,200 a, 200 b, and 200 c transmit. For example, the mobile station datatable 132 has an entry with Mobile Station ID=MS1, Transmission Power=2dBm, Maximum Transmission Power=20 dBm, and SINR=15 dB. In the presentcontext, mobile station IDs MS1, MS2, MS3, and MS4 correspond to mobilestations 200, 200 a, 200 b, and 200 c, respectively.

FIG. 9 illustrates a data structure of a data traffic size table. Thedata traffic size table 133 of FIG. 9 is stored in an appropriate memoryunder the management of the control unit 130. Specifically, the datatraffic size table 133 is formed from the following data fields: MobileStation ID, UL Data, and DL Data. The field values arranged in thehorizontal direction are associated with each other, thus forming asingle entry describing a specific mobile station.

The mobile station ID field contains an identifier of a specific mobilestation 200, 200 a, 200 b, and 200 c. The UL data field indicates theamount of data, in units of bytes, which the corresponding mobilestation is going to transmit in the next UL subframe. The DL data fieldindicates the amount of data, in units of bytes, which has to betransmitted to the corresponding mobile station in the next DL subframe.

The control unit 130 updates this data traffic size table 133 as theneed arises. More specifically, the UL data field is updated based oncontrol information received from the mobile stations 200, 200 a, 200 b,and 200 c. The DL data field is updated based on the current occupancyof the packet buffer 152 storing data packets. For example, the datatraffic size table 133 has an entry with Mobile Station ID=MS1, ULData=192 bytes, and DL Data=384 bytes.

The next section will now describe the detailed processing in thewireless communications system with the above-described features anddata structures. The description begins with a message flow between theradio base station 100 and mobile stations 200, 200 a, 200 b, and 200 cand then proceeds to a more specific explanation of the adaptivemodulation and coding control performed by the radio base station 100.

FIG. 10 is a sequence diagram illustrating an example process flow oftransmission power control. The following will describe the illustratedprocess of FIG. 10 in the order of step numbers, assuming that a mobilestation 200 is to make a first access to the radio base station 100.

[Step S11] The radio base station 100 continuously sends UL-MAP data,including location information of the ranging region, by using DLsubframes. Note that the radio base station 100 is not aware of themobile station 200 at this moment.

[Step S12] The mobile station 200 transmits a predetermined ranging codeto initiate a connection, by using the ranging region specified byUL-MAP data. Here the mobile station 200 determines its initialtransmission power level depending on the receive power level andquality of radio link signals received from the radio base station 100.

[Step S13] Based on the ranging code from the mobile station 200, theradio base station 100 measures the receive power level and receivetiming (on both the frequency axis and time axis) and identifies theirrespective differences from the desired receive power level and receivetiming. The radio base station 100 then sends an acknowledgment of thereceived ranging code back to the mobile station 200, including acommand to change the transmission power level and transmit timing onthe part of the mobile station 200.

Steps S12 and S13 are repeated until the mobile station 200 successfullyfinishes the adjustment of its transmission power level and transmittiming.

[Step S14] In order to execute an initial control procedure, includingassignment of CID to the mobile station 200, the radio base station 100allocates a UL-Burst region for the mobile station 200 to transmitcontrol information. The radio base station 100 then transmits UL-MAPdata indicating the allocation result.

It is noted here that the present explanation omits details of theinitial control procedure, except for those related to transmissionpower control.

[Step S15] Using the UL-Burst region specified in the received UL-MAPdata, the mobile station 200 transmits control information to the radiobase station 100 so as to indicate its current transmission power level,as well as its maximum possible transmission power level.

[Step S16] Based on the control information from the mobile station 200,the radio base station 100 updates its mobile station data table 132 andsends acknowledgment of the received control information back to themobile station 200.

[Step S17] The radio base station 100 may encounter the need for updatedtransmission power level information after the execution of step S16. Ifthis is the case, the radio base station 100 sends some controlinformation that requests the mobile station 200 to report itstransmission power level. For example, the radio base station 100 maysend such control information after a predetermined time since theprevious update of the transmission power level information. Here theradio base station 100 allocates a UL-Burst region for use by the mobilestation 200 to respond to the request, and transmits UL-MAP dataindicating the location of the UL-Burst region.

[Step S18] In response to the request for information from the radiobase station 100, the mobile station 200 transmits control informationindicating its current transmission power level, using the UL-Burstregion specified in the UL-MAP data.

The above steps permit the radio base station 100 to acquire informationon the current transmission power level and maximum transmission powerlevel of a mobile station 200 during their initial connection procedure.After that, the radio base station 100 collects the latest informationabout the transmission power level as occasion demands. Note that themaximum transmission power level will never change. Accordingly, thereis no need to update the maximum transmission power level, once it isobtained at the time of initial connection.

FIG. 11 is a sequence diagram illustrating an example process flow ofbandwidth allocation control. The following will describe theillustrated process of FIG. 11 in the order of step numbers, assumingthat a communication session is executed between the mobile station 200and radio base station 100.

[Step S21] When it has transmit data (user data and control information)to send to the radio base station 100, the mobile station 200 firstsends a bandwidth request ranging code (a ranging code to request abandwidth) to the radio base station 100 by using a ranging regionspecified in the received UL-MAP data.

[Step S22] Upon detection of the bandwidth request ranging code from themobile station 200, the radio base station 100 allocates a UL-Burstregion for use by the mobile station 200 to request allocation andtransmits UL-MAP data indicating the allocation result.

[Step S23] Using the UL-Burst region specified in the received UL-MAPdata, the mobile station 200 transmits control information thatindicates an allocation request, including information on the amount ofdata to be transmitted.

[Step S24] Based on the control information from the mobile station 200,the radio base station 100 updates its data traffic size table 133. Theradio base station 100 then allocates a UL-Burst region for use in datatransmission by the mobile station 200 and transmits UL-MAP dataindicating the allocation result.

[Step S25] The mobile station 200 executes data transmission by usingthe allocated UL-Burst region specified in the UL-MAP data. Here themobile station 200 may transmit some control information together withthe transmit data, in the case where it has pending transmit data thathas to be transmitted in the next and subsequent cycles. This controlinformation, referred to as a piggyback request, requests allocation ofresources for the next cycle.

[Step S26] The radio base station 100 receives payload data and controlinformation from the mobile station 200. Based on the received controlinformation, the radio base station 100 updates the data traffic sizetable 133. The radio base station 100 then allocates a UL-Burst regionfor use in data transmission by the mobile station 200 and transmitsUL-MAP data indicating the allocation result.

Steps S25 and S26 are repeated until the mobile station 200 has no morepending transmit data.

[Step S27] Similarly to step S26, the radio base station 100 updates thedata traffic size table 133 based on the received control information.The radio base station 100 then allocates a UL-Burst region for use indata transmission by the mobile station 200 and transmits UL-MAP dataindicating the allocation result.

[Step S28] The mobile station 200 executes data transmission by usingthe allocated UL-Burst region specified in the UL-MAP data. When thereis no more pending transmission data, the mobile station 200 stopstransmitting piggyback requests, thus terminating the successive datatransmission from the mobile station 200 to the radio base station 100.

According to the above steps, the mobile station 200 transmits apredetermined ranging code by using a ranging region, so as to notifythe radio base station 100 that the mobile station 200 intends toinitiate data transmission. The radio base station 100 first allocates aradio resource to the mobile station 200 for the purpose of itsallocation request. When an allocation request indicating the amount oftransmit data is received, the radio base station 100 allocates acorresponding amount of radio resources to the mobile station 200. Themobile station 200 thus transmits data by using the allocated radioresources. At the same time, the mobile station 200 may request anotherresource allocation for the next data transmission when it has morepending transmit data.

In the above-described embodiment, the mobile station 200 is configuredto transmit a bandwidth request ranging code to the radio base station100 to initiate data transmission. The embodiment may, however, bemodified such that the radio base station 100 sends queries to themobile station 200 at regular intervals to determine the presence oftransmit data.

FIG. 12 is a sequence diagram illustrating an example process flow of DLradio quality measurement. The following section will describe theillustrated process of FIG. 12 in the order of step numbers, assumingthat a communication session is executed between the mobile station 200and radio base station 100.

[Step S31] The radio base station 100 may encounter the need for updatedradio quality data of the mobile station 200. If this is the case, theradio base station 100 sends control information that requests themobile station 200 to report its quality measurement result. Forexample, the radio base station 100 sends such control information aftera predetermined time since the previous update to the radio qualitydata.

[Step S32] The radio base station 100 allocates a UL-Burst region foruse by the mobile station 200 to transmit its quality measurement resultand transmits UL-MAP data indicating the location of the UL-Burstregion.

[Step S33] In response to the request for information from the radiobase station 100, the mobile station 200 transmits control informationincluding radio quality data such as SINR, using the UL-Burst regionspecified in the UL-MAP data.

According to the above steps, the radio base station 100 collects thelatest radio quality data as necessary and updates its mobile stationdata table 132 with the collected data.

The next section will now describe the specifics of adaptive modulationand coding performed in the radio base station 100. The description willfirst present two control methods of adaptive modulation and coding foruplink communication, and then proceed to two control methods ofadaptive modulation and coding for downlink communication.

FIG. 13 is a flowchart illustrating a first UL profile setup process.The following will describe the illustrated process of FIG. 13 in theorder of step numbers.

[Step S41] Consulting the data traffic size table 133, the control unit130 selects one mobile station out of those scheduled to transmit datain the next radio frame.

[Step S42] With respect to the mobile station selected at step S41, thecontrol unit 130 examines its transmission power level seen in themobile station data table 132, as well as its amount of transmit dataseen in the data traffic size table 133. Based on these pieces ofinformation, the control unit 130 estimates a total power requirementfor each different burst profile defined in the profile candidate table131, assuming that those profiles are applied one by one to the selectedmobile station.

[Step S43] The control unit 130 evaluates the estimates of total powerrequirement that have been obtained at step S42 and chooses a burstprofile with the smallest estimate as a provisional burst profile forthe mobile station selected at step S41. Also the control unit 130calculates the number of slots required in the case where theprovisional burst profile is used.

[Step S44] The control unit 130 determines whether it has selected atstep S41 all the mobile stations scheduled to transmit data. If so, theprocess advances to step S45. If there are still pending mobilestations, the process proceeds to step S41.

[Step S45] Assuming the use of the provisional burst profile, thecontrol unit 130 determines whether it is possible to allocate all therequired slots in the UL-Burst region of the next radio frame. If it isfound possible to allocate those resources, the control unit 130 choosesthe provisional burst profiles as the final choice, thus terminating thepresent profile setup process. If it is found impossible to allocate allnecessary resources, the process advances to step S46.

[Step S46] The control unit 130 chooses a mobile station with thesmallest unit power requirement, from among the mobile stationsscheduled to transmit data in the next radio frame. Then the controlunit 130 chooses another burst profile one grade above the provisionalburst profile of the selected mobile station in terms of transmissionrates, and calculates again the number of required slots. The processthen proceeds to step S45.

According to the above steps, the radio base station 100 makes aprovisional selection of a burst profile for each mobile station havingdata to transmit, the provisional burst profile supposedly minimizingthe total power requirement during data transmission. The radio basestation 100 then determines whether it can allocate radio resources forthose provisional burst profiles. If it is not possible to allocatesufficient resources, the burst profile of a mobile station having asmaller unit power requirement is replaced with another burst profilewhose transmission rate is one grade higher than the current rate. Thisreplacement of burst profiles reduces the consumption of radioresources. The allocability of radio resources is then determined again,and if the result is positive, the provisional burst profiles aredetermined to be the final choice.

The above-described features make it possible to reduce the powerconsumption of the mobile stations 200, 200 a, 200 b, and 200 c as muchas possible, while ensuring that all radio resources can be allocated asneeded.

FIG. 14 illustrates a data structure of a power requirement table. Thispower requirement table is created for each individual mobile stationwhen the control unit 130 sets up a UL profile. The power requirementtable 134 illustrated in FIG. 14 is for the mobile station 200. Thepower requirement table 134 is formed from the following data fields:Profile, Subchannels, Unit Power Requirement, and Total PowerRequirement. The field values arranged in the horizontal direction areassociated with each other.

The profile field contains a character string indicating a modulationand coding scheme which may be used in a burst profile. Modulation andcoding schemes, each represented as a specific combination of modulationmethod, coding method, and coding rate, are registered in the profilecandidate table 131.

The subchannels field indicates the number of subchannels used at leastin data transmission. This number of subchannels can be calculated fromthe amount of data that the mobile station 200 is going to transmit andthe number of bits that can be conveyed by a slot. The latter parametermay vary depending on which modulation and coding scheme is used.

The unit power requirement field contains a value of required power persubchannel. Specifically, the burst profile QPSK(CC)1/2 has the lowesttransmission rate of all profiles in the table. The power requirement ofthis QPSK(CC)1/2 is equal to the transmission power level that themobile station 200 has reported. For the other burst profiles, theirrequired power values are obtained by adding some appropriate incrementsto the transmission power level reported by the mobile station 200. Takethe burst profile QPSK(CC)2/3 with the second to the lowest transmissionrate, for example. The required power of this burst profile iscalculated by adding 1.5 dBm to the required power of the burst profilewith the lowest transmission rate.

The control unit 130 has knowledge about how the required power levelsdiffer from burst profile to burst profile. Specifically, the unit powerrequirement varies in proportion to the transmission rate. That is, thehigher the transmission rate, the larger the unit power requirement.

The total power requirement field contains a value of total requiredpower, which is calculated from the number of subchannels and the unitpower requirement. More specifically, the total power requirement iscalculated by converting the given dBm value (logarithmic value) of unitpower requirement into a true value (non-logarithmic value), multiplyingit by the number of subchannels, and reconverting the product back to adBm value (logarithmic value). It is noted here that while the totalpower requirement generally tends to be proportional to the transmissionrate, their proportional relationship may not exactly be true when thenumber of subchannels is taken into consideration. In other words, theuse of a burst profile having the lowest transmission rate does notalways minimize the total power requirement.

The power requirement table 134 is compiled from data obtained at stepS42 of the foregoing UL profile setup process. For example, the controlunit 130 adds an entry that indicates: Profile=QPSK(CC)1/2,Subchannels=8, Unit Power Requirement=2 dBm, and Total PowerRequirement=11 dBm.

FIG. 15 illustrates a data structure of a UL profile setup table. The ULprofile setup table 135 of FIG. 15 is created by the control unit 130when it executes a UL profile setup process. This UL profile setup table135 is formed from the following data fields: Mobile Station ID,Profile, Unit Power Requirement, and Slot Allocation. The field valuesarranged in the horizontal direction are associated with each other,thus forming a single entry describing a specific mobile station.

The mobile station ID field contains an identifier of a specific mobilestation 200, 200 a, 200 b, and 200 c. The profile field contains acharacter string indicating a modulation and coding scheme which may beused in a burst profile. The unit power requirement field contains avalue of required power per subchannel in the case where the modulationand coding scheme specified in the profile field is at work. This valuecorresponds to one of those registered in the unit power requirementfield of the power requirement table 134. The slot allocation fieldindicates the number of slots that are necessary for data transmissionin the case where the modulation and coding scheme specified in theprofile field is at work.

The UL profile setup table 135 is compiled from data obtained at stepsS43 and S46 of the foregoing UL profile setup process. For example, thecontrol unit 130 adds an entry that indicates: Mobile. Station ID=MS1,Profile=QPSK(CC)1/2, Unit Power Requirement=2 dBm, and SlotAllocation=32.

FIG. 16 schematically illustrates a flow of a first UL profile setupprocess. Specifically, FIG. 16 illustrates UL profile setup tables 135a, 135 b, and 135 c as an example of how the UL profile setup table 135is changed during the UL profile setup process of FIG. 13.

As can be seen from the UL profile setup table 135 a, each mobilestation 200, 200 a, 200 b, and 200 c is provisionally assigned a burstprofile that minimize their total power requirement. Specifically, themobile stations 200, 200 b, and 200 c are assigned a burst profile usinga modulation and coding scheme of QPSK(CC)1/2, whereas the mobilestation 200 a is assigned a burst profile using a modulation and codingscheme of QPSK(CC)2/3.

Suppose now that the total number of slot allocations in the UL profilesetup table 135 a exceeds the number of slots allocable in the UL-Burstregion. This causes a change to the burst profile of a mobile stationhaving the smallest unit power requirement, as seen in the next ULprofile setup table 135 b. Specifically, the burst profile of the mobilestation 200 is changed from the one with a unit power requirement of 2dBm to QPSK(CC)2/3, whose transmission rate is one grade higher than theoriginal rate. This change in the profile field also affects the unitpower requirement field and the slot allocation field.

Even with the UL profile setup table 135 a, however, the total number ofslot allocations may still exceed the number of slots allocable in theUL-Burst region. If this is the case, an additional change is made tothe burst profile of a mobile station having the smallest unit powerrequirement, as seen in the next UL profile setup table 135 c.Specifically, the burst profile of another mobile station 200 c ischanged from the one with a unit power requirement of 3 dBm toQPSK(CC)2/3, whose transmission rate is one grade higher than theoriginal rate. This change in the profile field also affects the unitpower requirement field and the slot allocation field.

As can be seen from the above example, each mobile station is firstassigned a provisional burst profile with a minimum total powerrequirement. If it is not possible to allocate sufficient radioresources, then the transmission rate is raised by one grade for themobile station having the smallest unit power requirement at thatmoment. This is repeated until all the necessary radio resources arefound allocable. The result is minimized power consumption in eachmobile station. It is noted that the above-described operation ofraising transmission rates is applied to a different mobile station eachtime, because the unit power requirement is increased by a raisedtransmission rate.

FIG. 17 is a flowchart of a second UL profile setup process. Thefollowing will describe the illustrated process of FIG. 17 in the orderof step numbers.

[Step S51] Consulting the data traffic size table 133, the control unit130 selects one mobile station out of those scheduled to transmit datain the next radio frame.

[Step S52] With respect to the mobile station selected at step S51, thecontrol unit 130 examines its transmission power level seen in themobile station data table 132. Based on this information, the controlunit 130 estimates a unit power requirement for each different burstprofile defined in the profile candidate table 131, assuming that thoseprofiles are applied one by one to the selected mobile station. That is,the control unit 130 creates a table similar to the foregoing powerrequirement table 134. It is, however, not necessary to calculate totalpower requirement.

[Step S53] Of all burst profiles defined in the profile candidate table131, the control unit 130 makes a provisional selection of a burstprofile with the lowest transmission rate and assigns it to the mobilestation selected at step S51. Also the control unit 130 calculates thenumber of required slots in the case where the provisional burst profileis used. That is, the control unit 130 creates and updates the foregoingUL profile setup table 135.

[Step S54] The control unit 130 determines whether it has selected atstep S51 all the mobile stations scheduled to transmit data. If so, theprocess advances to step S55. If there are pending mobile stations, theprocess proceeds to step S51.

[Step S55] Assuming the use of the assigned provisional burst profiles,the control unit 130 determines whether it is possible to allocate allthe necessary slots in the UL-Burst region of the next radio frame. Ifit is found possible to allocate them, the control unit 130 chooses theprovisional burst profiles as the final choice, thus terminating thepresent profile setup process. If it is found impossible to allocatesufficient slots, the process advances to step S56.

[Step S56] The control unit 130 chooses a mobile station with thesmallest unit power requirement, from among the mobile stationsscheduled to transmit data in the next radio frame. Then the controlunit 130 replaces the provisional burst profile with an upper-boundburst profile applicable to the selected mobile station, and itcalculates again the number of necessary slots, assuming the new burstprofile. The process then returns to step S55. Here the term“upper-bound burst profile” refers to a burst profile having the highesttransmission rate, of all the burst profiles whose unit powerrequirement does not exceed the maximum transmission power seen in themobile station data table 132.

According to the above steps, the mobile stations having data totransmit are first assigned a provisional burst profile with the lowesttransmission rate. It is then determined whether radio resources areallocable for those provisional burst profiles. If it is not possible toallocate sufficient resources, the burst profile of a mobile stationwith a smaller unit power requirement is replaced with another burstprofile having the highest applicable transmission rate. Thisreplacement of burst profiles alleviates the radio resourcerequirements. The allocability of radio resources is then determinedagain, and if the result is positive, the provisional burst profiles aredetermined to be the final choice.

It is therefore possible to control the power consumption of mobilestations 200, 200 a, 200 b, and 200 c while ensuing that all resourcescan be allocated as needed. At the preceding step (first step), the basestation provisionally selects a burst profile with the lowesttransmission rate under the assumption that such a bust profile wouldminimize the total power requirement. This method accelerates theprocessing since it does not actually calculate total power requirement.At the succeeding step (second step), the transmission rate is raised,not stepwise, but right up to the upper bound, thus finishing theoperation more quickly.

FIG. 18 schematically illustrates a flow of the second UL profile setupprocess. Specifically, FIG. 18 illustrates UL profile setup tables 135d, 135 e, and 135 f as an example of how the UL profile setup table 135is changed during the UL profile setup process discussed in FIG. 17.

As can be seen from the UL profile setup table 135 d, each mobilestation 200, 200 a, 200 b, and 200 c is provisionally assigned a burstprofile with the lowest transmission rate. Specifically, the mobilestations 200, 200 a, 200 b, and 200 c are each assigned a modulation andcoding scheme of QPSK(CC)1/2 as their provisional burst profile.

Suppose now that the total number of slot allocations in the UL profilesetup table 135 d exceeds the number of slots allocable in the UL-Burstregion. This causes a change to the burst profile of a mobile stationhaving the smallest unit power requirement, as seen in the next ULprofile setup table 135 e. Specifically, the burst profile of the mobilestation 200 is changed from the one with a unit power requirement of 2dBm to another profile 16QAM(CC)3/4, whose transmission rate is thehighest of all applicable burst profiles within the limit of maximumtransmission power (20 dBm). This change in the profile field alsoaffects the unit power requirement field and the slot allocation field.

Even with the UL profile setup table 135 e, however, the total number ofslot allocations may still exceed the number of slots allocable in theUL-Burst region. If this is the case, an additional change is made tothe burst profile of a mobile station having the smallest unit powerrequirement, as seen in the next UL profile setup table 135 f.Specifically, the burst profile of the mobile station 200 a is changedfrom the original one with a unit power requirement of 3 dBm to anotherprofile QPSK(CC)3/4, whose transmission rate is the highest of allapplicable burst profiles within the limit of maximum transmission power(8 dBm). This change in the profile field also affects the unit powerrequirement field and the slot allocation field.

As can be seen from the above example, each mobile station is firstassigned a provisional burst profile with the lowest transmission rate.If it is not possible to allocate sufficient radio resources, then thebase station identifies a mobile station having the smallest unit powerrequirement at the moment, and raises its transmission rate to the upperbound. This operation is repeated until all necessary radio resourcesare found allocable, thereby controlling the power consumption in eachmobile station.

According to another example of the UL profile setup process, the firsthalf of the first method illustrated in FIG. 13 may be swapped with thatof the second method illustrated in FIG. 17. That is, burst profilesthat minimize the total power requirement of mobile stations areselected provisionally, and their transmission rates are then changedright up to the upper bound as necessary. It may also be possible toselect provisional burst profiles with the lowest transmission rate, andthen increase the transmission rates in a stepwise fashion. As can beseen from those examples, the selection of a processing method in thefirst half can be made independently of that in the second half.

FIG. 19 is a flowchart of a first DL profile setup process. Thefollowing will describe the illustrated process of FIG. 19 in the orderof step numbers.

[Step S61] Consulting the data traffic size table 133, the control unit130 identifies mobile stations to which data will be transmitted in thenext radio frame. The control unit 130 then makes a provisionalselection of a burst profile for each identified mobile station, bychoosing the one with the lowest transmission rate from among thosedefined in the profile candidate table 131. Also the control unit 130calculates the number of required subchannels, assuming the use of thoseprovisional burst profiles.

[Step S62] The control unit 130 determines whether it is possible toallocate all necessary subchannels in the DL-Burst region of the nextradio frame. If it is found possible to allocate all necessarysubchannels, the control unit 130 chooses the provisional burst profilesas the final choice, thus exiting from the present profile setupprocess. If it is found impossible to allocate sufficient subchannels,the process advances to step S63.

[Step S63] The control unit 130 extracts mobile stations having thelowest transmission rate in their provisional burst profiles. In thecase where two or more such mobile stations are found, the control unit130 then extracts one of those mobile stations that has the highestSINR, by consulting the mobile station data table 132.

[Step S64] With respect to the mobile station extracted at step S63, thecontrol unit 130 changes its provisional burst profile to another burstprofile whose transmission rate is one grade higher than the currentrate. The process then returns to step S62.

According to the above steps, the radio base station 100 assigns aprovisional burst profile with the lowest transmission rate to eachdestination mobile station to which the radio base station 100 transmitsdata. The radio base station 100 then determines whether radio resourcesare allocable for those provisional burst profiles. If it is notpossible to allocate sufficient resources, the provisional burst profileof a mobile station having a higher SINR (i.e., higher radio linkquality) is replaced with another burst profile whose transmission rateis one grade higher than the current rate. This replacement of burstprofiles alleviates the radio resource requirements. The allocability ofradio resources is then determined again, and if the result is positive,the provisional burst profiles are determined to be the final choice.

The above-described features make it possible to reduce the transmissionrates per unit resource as much as possible, while ensuring thatsufficient radio resources can be allocated for complete transmission ofdata to the mobile stations 200, 200 a, 200 b, and 200 c.

FIG. 20 illustrates a data structure of a DL profile setup table. The DLprofile setup table 136 of FIG. 20 is created by the control unit 130when it executes a DL profile setup process. Specifically, the DLprofile setup table 136 is formed from the following data fields:Profile, Mobile Station ID, Total Data Size, and Subchannels. The fieldvalues arranged in the horizontal direction are associated with eachother.

The profile field contains a character string indicating a modulationand coding scheme which may be used in a burst profile. This modulationand coding scheme is among those listed in the profile candidate table131. The mobile station ID field contains identifiers of specific mobilestations to which the modulation and coding scheme in the profile filedis to be applied. The total data size field contains a value indicatingthe total amount of transmit data destined for the mobile stations seenin the mobile station ID field. The subchannels field indicates thenumber of subchannels necessary for transmission of as much data asspecified in the total data size field. This number of subchannels iscalculated from the amount of transmit data and the number of bits thatcan be conveyed by a single subchannel, where the latter parameterdepends on which modulation and coding scheme is used.

The DL profile setup table 136 is compiled from data obtained at stepsS61 and S64 in the foregoing DL profile setup process. For example, thecontrol unit 130 adds an entry that indicates: Profile=QPSK(CC)1/2,Mobile Station ID=(MS1, MS2, MS3, MS4), Total Data Size=928 bytes, andSubchannels=11. It is noted that the DL profile setup table 136 has adifferent data structure from the foregoing UL profile setup table 135.This is because the DL-Burst region carries transmit data by combiningmultiple data using the same modulation and coding scheme into a singleblock.

FIG. 21 schematically illustrates a flow of the first DL profile setupprocess. Specifically, FIG. 21 illustrates DL profile setup tables 136 aand 136 b as an example of how the DL profile setup table 136 is changedduring the DL profile setup process discussed in FIG. 19.

As can be seen from the DL profile setup table 136 a, each mobilestation 200, 200 a, 200 b, and 200 c is provisionally assigned a burstprofile with a minimum transmission rate. Specifically, the mobilestations 200, 200 a, 200 b, and 200 c are assigned a modulation andcoding scheme of QPSK(CC)1/2 as their provisional burst profiles.

Suppose now that the total number of subchannels in the DL profile setuptable 136 a exceeds the number of subchannels allocable in the DL-Burstregion. This causes a change to the burst profile of a mobile stationhaving the highest SINR of those having the lowest transmission rate, asseen in the next DL profile setup table 136 b. Specifically, the mobilestation 200 has an SINR of 15 dB, which is the highest of all the mobilestations 200, 200 a, 200 b, and 200 c. Accordingly, the burst profile ofthis mobile station 200 is changed to QPSK(CC)2/3, whose transmissionrate is one grade higher than the original rate. This change alsoaffects the total data size and required subchannels of each relevantburst profile.

As can be seen from the above example, each mobile station is firstassigned a provisional burst profile with the lowest transmission rate.If it is not possible to allocate sufficient radio resources, then thetransmission rate is raised by one grade for the mobile station havingthe lowest transmission rate and highest SINR at that moment. Thisoperation is repeated until all the radio resources are found allocable.These features make it possible to transmit data addressed todestination mobile stations at as low transmission rate per unitresource as possible, thus increasing the probability of successful datareception at the destination mobile stations.

FIG. 22 is a flowchart of a second DL profile setup process. Thefollowing will describe the illustrated process of FIG. 22 in the orderof step numbers.

[Step S71] Consulting the data traffic size table 133, the control unit130 identifies mobile stations to which data will be transmitted in thenext radio frame. The control unit 130 then makes a provisionalselection of a burst profile for each identified mobile station, bychoosing the one with the lowest transmission rate from among thosedefined in the profile candidate table 131. Also the control unit 130calculates the number of required subchannels, assuming the use of thoseprovisional burst profiles.

[Step S72] The control unit 130 determines whether it is possible toallocate all necessary subchannels in the DL-Burst region of the nextradio frame. If it is found possible to allocate all necessarysubchannels, the control unit 130 chooses the provisional burst profilesas the final choice, thus terminating the present profile setup process.If it is found impossible to allocate sufficient subchannels, theprocess advances to step S73.

[Step S73] The control unit 130 extracts mobile stations having thelowest transmission rate in their provisional burst profiles. In thecase where two or more such mobile stations are found, the control unit130 then extracts one of those mobile stations that has the highestSINR, by consulting the mobile station data table 132.

[Step S74] With respect to the mobile station extracted at step S73, thecontrol unit 130 changes its provisional burst profile to an upper-boundburst profile that is applicable to that mobile station. The processthen returns to step S72. The term “upper-bound burst profile” refersherein to a burst profile whose transmission rate is the highest of allburst profiles whose SINR seen in the mobile station data table 132satisfies the conditions of SINR Threshold described in the profilecandidate table 131.

According to the above steps, the radio base station 100 first assigns aprovisional burst profile with the lowest transmission rate to eachdestination mobile station to which the radio base station 100 transmitsdata. The radio base station 100 then determines whether radio resourcesare allocable for those provisional burst profiles. If it is notpossible to allocate sufficient resources, the radio base station 100identifies a mobile station having a low transmission rate in itsprovisional burst profile and indicating a high SINR (i.e., high radiolink quality). The burst profile of this mobile station is then replacedwith another burst profile having the highest applicable transmissionrate. This replacement of burst profiles alleviates the radio resourcerequirements. The allocability of radio resources is then determinedagain, and if the result is positive, the radio base station 100determines the provisional burst profiles as the final choice.

The above-described features make it possible to reduce the transmissionrates per unit resource as much as possible, while ensuring thatsufficient radio resources can be allocated for complete transmission ofdata to the mobile stations 200, 200 a, 200 b, and 200 c. Whennecessary, the transmission rate is raised, not stepwise, but right upto the upper bound, thus finishing the operation more quickly.

FIG. 23 schematically illustrates a flow of the second DL profile setupprocess. Specifically, FIG. 23 illustrates DL profile setup tables 136 cand 136 d as an example of how the DL profile setup table 136 is changedduring the DL profile setup process discussed in FIG. 22.

As can be seen from the DL profile setup table 136 c, each mobilestation 200, 200 a, 200 b, and 200 c is provisionally assigned a burstprofile with a minimum transmission rate. Specifically, the mobilestations 200, 200 a, 200 b, and 200 c are assigned a modulation andcoding scheme of QPSK(CC)1/2 as their provisional burst profiles.

Suppose now that the total number of subchannels in the DL profile setuptable 136 c exceeds the number of subchannels allocable in the DL-Burstregion. This causes a change to the burst profile of a mobile stationhaving the highest SINR of those having the lowest transmission rate, asseen in the next DL profile setup table 136 d. Specifically, the mobilestation 200 has an SINR of 15 dB, which is the highest of all the mobilestations 200, 200 a, 200 b, and 200 c. The burst profile of this mobilestation 200 is thus changed to 16QAM(CC)3/4 which offers the highesttransmission rate while satisfying the conditions of SINR threshold.This change also affects the total data size and required subchannels ofeach relevant burst profile.

As can be seen from the above example, each mobile station is firstassigned a provisional burst profile with the lowest transmission rate.If it is not possible to allocate sufficient radio resources, then thetransmission rate is raised to the upper bound for the mobile stationhaving the lowest transmission rate and highest SINR at that moment.This operation is repeated until all necessary radio resources are foundallocable. These features make it possible to transmit data addressed todestination mobile stations at as low transmission rate as possible,thus increasing the probability of successful data reception at thedestination mobile stations.

The above-described features of the proposed wireless communicationssystem enable the radio base station 100 to select more appropriatemodulation and coding schemes, considering the viewpoint of mobilestations 200, 200 a, 200 b, and 200 c that the radio base station 100 isserving.

In uplink communication, the system controls the total transmissionpower of each mobile station 200, 200 a, 200 b, and 200 c, whileensuring the allocation of sufficient radio resources for completereception of their transmit data. This also means reduction of powerconsumption in those mobile stations 200, 200 a, 200 b, and 200 c.

In downlink communication, the system controls itself to lower thetransmission rates as much as possible, while ensuring the allocation ofsufficient radio resources for complete transmission of data to mobilestations 200, 200 a, 200 b, and 200 c. This increases the probability ofsuccessful reception of signals at the mobile stations 200, 200 a, 200b, and 200 c, thus contributing to more stable operation of wirelesscommunication.

The foregoing embodiments have been discussed using an example of amobile communications system formed from a radio base station and mobilestations. The proposed control methods of adaptive modulation and codingcan easily be applied to other kinds of communications systems such as awireless communications system. The foregoing embodiments also assumeIEEE 802.16e as the underlying communication standard. The proposedcontrol methods of adaptive modulation and coding, however, can also beimplemented with other standard specifications, particularly with thoseother than the TDD technique.

Further, the control methods of the above embodiments are not limited bythe foregoing specific modulation and coding schemes. More particularly,the burst profiles may incorporate only one or two of modulation method,coding method, and coding rate as variable elements, while using therest as fixed elements. The above embodiments also assume that differentmodulation and coding schemes may be selected for uplink communicationand downlink communication. The embodiments may, however, be configuredto use the same modulation and coding scheme for both uplinkcommunication and downlink communication. The above embodiments may alsobe modified such that mobile stations will report their transmissionpower levels to the radio base station on a per-subcarrier basis,instead of on a per-subchannel basis.

The above-noted receiving apparatus, transmitting apparatus, receptionmethod, and transmission method make it possible to select appropriatemodulation and coding schemes, considering also the viewpoint of remotecommunication devices.

All examples and conditional language recited herein are intended forpedagogical purposes to aid the reader in understanding the inventionand the concepts contributed by the inventor to furthering the art, andare to be construed as being without limitation to such specificallyrecited examples and conditions, nor does the organization of suchexamples in the specification relate to a showing of the superiority andinferiority of the invention. Although the embodiment(s) of the presentinvention has(have) been described in detail, it should be understoodthat various changes, substitutions and alterations could be made heretowithout departing from the spirit and scope of the invention.

What is claimed is:
 1. A transmitting apparatus that assigns modulationand coding schemes respectively to a plurality of receiving apparatusesand transmits data to the receiving apparatuses by using the assignedmodulation and coding schemes, the transmitting apparatus comprising: acontrol unit that identifies the amount of data to be transmitted toeach receiving apparatus; selects, for each individual receivingapparatus, a modulation and coding scheme that transports a smalleramount of data per unit resource than the other modulation and codingschemes, from among a plurality of candidates for the modulation andcoding schemes; determines whether necessary resources are allocable fortransmission of the data to the receiving apparatuses, based on theamount of the data to be transmitted and the selected modulation andcoding schemes; and when the resources are unallocable, changes thecurrently selected modulation and coding scheme of at least one of thereceiving apparatuses to another modulation and coding scheme thattransports a larger amount of data per unit resource than the currentlyselected modulation and coding scheme.
 2. The transmitting apparatusaccording to claim 1, wherein the control unit further collectsinformation on receive signal quality of each receiving apparatus, andchanges the modulation and coding scheme of a receiving apparatus havinga higher receive signal quality than the other receiving apparatuses,when the resources are unallocable.
 3. The transmitting apparatusaccording to claim 1, wherein the control unit changes, when theresources are unallocable, the modulation and coding schemes byincreasing the amount of transported data per unit resource in astepwise manner, until the resources are found allocable.
 4. Thetransmitting apparatus according to claim 1, wherein the control unitchanges, when the resources are unallocable, the modulation and codingscheme of at least one of the receiving apparatuses to anothermodulation and coding scheme that transports a highest amount of dataper unit resource, of all the modulation and coding schemes applicableto said at least one of the transmitting apparatuses.
 5. A transmissionmethod for assigning modulation and coding schemes respectively to aplurality of receiving apparatuses and transmitting data to thereceiving apparatuses by using the assigned modulation and codingschemes, the transmission method comprising: identifying the amount ofdata to be transmitted to each receiving apparatus; selecting, for eachindividual receiving apparatus, a modulation and coding scheme thattransports a smaller amount of data per unit resource than the othermodulation and coding schemes, from among a plurality of candidates forthe modulation and coding schemes; determining whether necessaryresources are allocable for transmission of the data to the receivingapparatuses, based on the amount of the data to be transmitted and theselected modulation and coding schemes; and changing, when the resourcesare unallocable, the currently selected modulation and coding scheme ofat least one of the receiving apparatuses to another modulation andcoding scheme that transports a larger amount of data per unit resourcethan the currently selected modulation and coding scheme.